Lasing in metal-insulator-metal sub-wavelength plasmonic waveguidesHill, M.T.; Marell, M.J.H.; Leong, E.S.P.; Smalbrugge, E.; Zhu, Y.C.; Sun, Minghua; Veldhoven, van, P.J.; Geluk, E.J.; Karouta, F.; Oei, Y.S.; Nötzel, R.; Ning, C.Z.; Smit, M.K.

We demonstrated a general methodology of growing spatially composition-controlled alloys by combining spatial source reagent gradient with a temperature gradient. Using this dual gradient method, we achieved for the first time a continuous spatial composition grading of single-crystal quaternary Zn(x)Cd(1-x)S(y)Se(1-y) alloy nanowires over the complete band gap range along the length of a substrate. The band gap grading spans between 3.55 eV (ZnS) and 1.75 eV (CdSe) on a single substrate, with the corresponding light emission over the entire visible spectrum. We also showed that the dual gradient method can be extended to achieve alloy composition control in two spatial dimensions. The unique material platform achieved will open a wide range of applications from color engineered display and lighting, full spectrum solar cells, multispectral detectors, or spectrometer on-a-chip to superbroadly tunable nanolasers. The growth methodology can be extended more generally to other alloy systems.

Surface states in semiconductor nanowires (NWs) are detrimental to the NW optical and electronic properties and to their light emission-based applications, due to the large surface-to-volume ratio of NWs and the congregation of defects states near surfaces. In this paper, we demonstrated an effective approach to eliminate surface states in InAs NWs of zinc-blende (ZB) and wurtzite (WZ) structures and a dramatic recovery of band edge emission through surface passivation with organic sulfide octadecylthiol (ODT). Microphotoluminescence (PL) measurements were carried out before and after passivation to study the dominant recombination mechanisms and surface state densities of the NWs. For WZ-NWs, we show that the passivation removed the surface states and recovered the band-edge emission, leading to a factor of ∼19 reduction of PL linewidth. For ZB-NWs, the deep surface states were removed and the PL peaks width became as narrow as ∼250 nm with some remaining emission of near band-edge surface states. The passivated NWs showed excellent stability in atmosphere, water, and heat environments. In particular, no observable changes occurred in the PL features from the passivated NWs exposed in air for more than five months.

We used an improved cothermal evaporation route for the first time to achieve quaternary semiconductor nanostructured alloys, using an example of Zn(x)Cd(1-x)S(y)Se(1-y) nanobelts. The PL (bandgap) of these as-grown nanostructured alloys can be continuously tunable across the entire visible spectrum through experimentally controlling their compositions. Such widely controlled alloy nanostructures via composition/light emission provide a new material platform for applications in wavelength-tunable lasers, multicolor detectors, full-spectrum solar cells, LEDs, and color displays.

The electrochemical deposition and dissolution of lead on gold electrodes immersed in an aqueous solution of lead nitrate were studied in situ using a biasing liquid cell by transmission electron microscopy (TEM). We investigate in real time the growth mechanisms of lead dendrites as deposited on the electrodes under an applied potential. TEM images reveal that lead dendrites are developed by the fast protrusion of lead branches in the electrolyte and tip splitting. And, the fast growing tip of the dendritic branch is composed of polycrystalline nanograins and it develops into a single crystalline branch eventually. This study demonstrated unique electrochemical growth of single crystal dendrites through nucleation, aggregation, alignment and attachment of randomly oriented small grains. Additionally, we found the lead concentration in the electrolyte drastically influences the morphology of dendritic formation.